One of the goals of plant genetic engineering is to produce plants with agronomically desirable characteristics or traits. The proper expression of a desirable transgene in a transgenic plant is one way to achieve this goal. Regulatory elements such as promoters, leaders, and introns are non-coding polynucleotide molecules which play an integral part in the overall expression of genes in living cells. Isolated regulatory elements that function in plants are therefore useful for modifying plant phenotypes through the methods of genetic engineering.
Many regulatory elements are available and are useful for providing good overall expression of a transgene. For example, constitutive promoters such as P-FMV, the promoter from the 35S transcript of the Figwort mosaic virus (U.S. Pat. No. 6,051,753);P-CaMV 35S, the promoter from the 35S RNA transcript of the Cauliflower mosaic virus (U.S. Pat. No. 5,530,196); P-Rice Actin 1, the promoter from the actin 1 gene of Oryza sativa (U.S. Pat. 5,641,876); and P-NOS, the promoter from the nopaline synthase gene of Agrobacterium tumefaciens are known to provide some level of gene expression in most or all of the tissues of a plant during most or all of the plant's lifespan. While previous work has provided a number of regulatory elements useful to affect gene expression in transgenic plants, there is still a great need for novel regulatory elements with beneficial expression characteristics. Many previously identified regulatory elements fail to provide the patterns or levels of expression required to fully realize the benefits of expression of selected genes in transgenic crop plants.
Spatial organization within the eukaryotic cell and directed movements of the cell contents are mediated by the cytoskeleton, a network of filamentous protein polymers that permeates the cytosol. Actin is one of the three major families of proteins making up the cytoskeleton. Members of this multi-gene family have been reported in almost all eukaryotic species including yeast, humans, mouse, Drosophila, tobacco, maize, rice, soybean, potato and Arabidopsis. Plant actins are encoded by a multi-gene family, constituted by a number of different isotypes.
We hypothesized that the regulatory elements from an actin gene might have a constitutive expression pattern and that the regulatory elements could be useful to direct expression of a transgene such as a glyphosate resistant 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) transgene to produce a glyphosate tolerant plant. The efficient production of glyphosate tolerant plants requires the use of regulatory elements capable of directing transgene expression in all tissues including the most sensitive reproductive organs such as anthers and meristem tissues. The present invention thus provides such regulatory elements isolated from actin genes of Oryza sativa and Zea mays. 